Biological Regeneration in Vascular Grafts

Mammarian arteries are preferable for coronary artery bypass grafting. However vein grafts are more commonly used because multiple grafts are frequently needed. Arterial grafts are preferred because the patency rate is 93%. Vein grafts have only 45% patency after seven years (Lytle, 1985). This disturbing result using vein grafts in a large population of patients is likely related to damage of the vein walls, caused by the high pressures to which the veins are subjected, during harvesting and implantation. This leads to endothelial desquamation and an inflammatory reaction in the distended wall. A sequence of biological responses is evoked. A deposition of a platelet/fibrin layer occurs and then endothelial and smooth muscle cells are stimulated to restore the defect. Optimally this biological response of regeneration results in re-endothelialization and in smooth muscle cell proliferation, commonly named arterialization of the graft. However vein grafts frequently occlude early, because of thrombosis, or later due to excessive smooth muscle cell proliferation. Thus distension of a vein graft by the arterial pressure damages the vein wall, which affects patency, but also stimulates a biological mechanism of adaptation of the vein graft to the arterial pressure, i.e. arterialization. Ideally damage of the vein graft should be prevented but the mechanism to adapt to the higher pressure should be preserved.